The invention relates to electronic crash detection systems for vehicles, and more specifically to the acceleration sensors used with the electronic crash detection systems.
Electronic crash detection systems utilize acceleration sensors to detect if a vehicle is involved in a crash. In the event of a crash, restraint devices are deployed to protect the occupants of the vehicle. Traditionally, a central control unit located within the passenger compartment of the vehicle contains one or more accelerometers that measure the deceleration within the passenger compartment. If the deceleration threshold is reached, the restraints are deployed.
More recently, additional peripheral accelerometers are being mounted in various locations on the frame of the vehicle to improve the performance of the crash detection systems. For example, additional accelerometers may be located in the crumple zones of the vehicle. Furthermore, additional accelerometers may be located on the sides of the vehicle to detect side impacts. Currently, most peripheral acceleration sensors used with crash detection systems are mounted to the vehicle""s frame with screws or bolts.
It is important to ensure that each sensor is properly mounted on the vehicle and that each sensor remains properly mounted over the operational lifetime of the vehicle. Proper mounting of the sensors is crucial for the proper functioning of the crash detection systems. If a sensor is improperly mounted or later becomes loose, the measured acceleration signals will not be accurate and the crash detection system may not function as intended.
One commonly used method to ensure proper sensor mounting is to detect an electric ground between the sensor and the mounting location. This method assumes that the sensor must be properly affixed to the vehicle to maintain an electrical connection between the sensor and the frame. If the electrical connection is broken, the sensor is determined to be separated from the frame.
Other methods used in the art include sending a vibrational/acoustical test signal to the sensor, thereby causing the sensor to resonate and produce an output signal that can be measured and compared to predetermined values to determine if the sensor is properly mounted. U.S. Pat. Nos. 4,950,915, 5,373,722 and 5,457,982 disclose examples of these methods.
These prior art methods of ensuring proper sensor mounting present various problems. For example, the method of detecting an electrical ground between the sensor and the mounting location requires the installation of specific detection hardware. This increases the material and manufacturing costs for the system and makes the system more difficult to install. Furthermore, this prior art method is not able to distinguish between a properly mounted sensor and a loose sensor when the electrical connection for the loose sensor remains at least partially intact.
The other methods utilizing acoustical/vibrational signal comparisons require the installation of various types of signal generators for producing the test signals. This increases the material and manufacturing costs for the system and makes the system more difficult to install.
In light of these problems, the present invention provides a method and system of ensuring proper sensor mounting by monitoring the noise levels of the signals generated by the acceleration sensors. All driving conditions generate vibrations in a vehicle that cause a certain level of xe2x80x9cnoisexe2x80x9d in the measured acceleration signals. A loose sensor will generate a higher level of noise than a properly mounted sensor. By monitoring the noise levels of different acceleration sensors and comparing those monitored levels with a predetermined noise threshold or with the noise levels of one or more counterpart sensors, a loose sensor can be detected.
The method and system of the present invention is less expensive to implement and is more reliable than previous methods because little or no additional hardware is required for implementation. The same processor used to interpret the acceleration signals can be used to monitor and compare the noise levels present in the signals.
More specifically, the invention provides a method of detecting the improper mounting of a sensor on a motor vehicle where the sensor emits output signals. The method comprises the steps of monitoring the output signals of the sensor, determining the noise levels in the output signals and comparing the noise levels from the output signals to a threshold noise value to determine if the sensor is properly mounted.
In one aspect of the invention, the threshold noise value can be predetermined based on vehicle characteristics or can be determined from another sensor mounted on the vehicle. In another aspect of the invention, the sensors will issue a warning when the noise levels exceed the threshold noise value. In yet another aspect of the invention, the sensors will increment a counter each time the threshold value is exceeded and will issue a warning when the counter is incremented a predetermined number of times.
The present invention also provides another method for detecting the improper mounting of a sensor on a motor vehicle having a first sensor and a second sensor. Each sensor emits output signals. The method comprises the steps of monitoring the output signals of the sensors, determining the noise levels in the output signals being emitted by each of the sensors and comparing the noise levels of the first sensor to the noise levels of the second sensor to determine if the sensors are properly mounted.
In one aspect of the invention, the vehicle has a longitudinal axis and comparing the noise levels of the sensors includes comparing the noise levels of two sensors that are positioned in substantially mirrored relation with respect to the longitudinal axis. In another aspect of the invention, the noise level of the first sensor is compared to a threshold value and a counter is incremented when the threshold value is exceeded. The noise level of the second sensor is also compared to a predetermined threshold value and a second counter is incremented when the threshold value is exceeded. The first and second counters are then compared to determine whether one of the sensors may be improperly mounted. A warning is issued when a sensor is determined to be improperly mounted.
In yet another aspect of the invention, determining the noise levels of the output signals can include filtering the signals. The signals can be filtered using a band-pass filter or a high-pass filter. The filtered output signals are then integrated and compared to determine whether there is an improperly mounted sensor.
In another aspect of the invention, the noise levels of sensors that are not positioned in substantially mirrored relation with respect to the longitudinal axis are compared by equalizing the noise levels of the two sensors. The noise levels are equalized using correction factors that are determined such that under normal driving conditions, the noise levels of the two sensors will be substantially equal.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.